1. Field of the Invention
The present invention relates to an anisotropically conductive sheet suitable for use, for example, in electrical connection between circuit devices such as electronic parts, or as a connector in inspection apparatus for circuit devices such as printed circuit boards and semiconductor integrated circuits, a production process thereof, and a connector.
2. Description of the Background Art
An anisotropically conductive elastomer sheet has a conductor exhibiting conductivity only in its thickness-wise direction or a pressure-conductive conductor exhibiting conductivity only in its thickness-wise direction when it is pressurized in the thickness-wise direction. Since the anisotropically conductive elastomer sheet has features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection is feasible with mechanical shock or strain absorbed therein, it is widely used as a connector for achieving electrical connection between a circuit device, for example, a printed circuit board, and a leadless chip carrier, liquid crystal display panel or the like in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
The anisotropically conductive elastomer sheet is also used as a sensor for detecting external force in a key board, touch switch or the like.
Further, in electrical inspection for electronic circuits or semiconductor integrated circuits fabricated by various materials in accordance with various methods, such as printed circuit boards, flexible boards, ceramic boards or a carrier tape for TAB, or MCM in which a plurality of semiconductor integrated circuits are incorporated into a module, it is conducted to interpose an anisotropically conductive elastomer sheet between an electrode region to be inspected and an electrode region for inspection in order to achieve electrical connection between electrodes to be inspected formed on at least one surface of a circuit device which is a inspection subject and electrodes for inspection formed on the surface of a circuit board for inspection.
As such anisotropically conductive elastomer sheets, there have heretofore been known those of various structures. For example, Japanese Patent Application Laid-Open No. 93393/1976 discloses anisotropically conductive elastomer sheets obtained by uniformly dispersing metal particles in an elastomer, Japanese Patent Application Laid-Open No. 147772/1978 discloses anisotropically conductive elastomer sheets obtained by unevenly distributing particles of a conductive magnetic material in an elastomer to form many conductive path-forming parts extending in the thickness-wise direction thereof and insulating parts for mutually insulating them, and Japanese Patent Application Laid-Open No. 250906/1986 discloses anisotropically conductive elastomer sheets with a difference in level defined between the surface of the conductive path-forming parts and the insulating parts.
However, since an anisotropically conductive sheet has conductivity in its thickness-wise direction and insulating property in its plane direction, static electricity is generated on the surface of the anisotropically conductive sheet according to manner of usage or service environment to offer various problems due to charging.
For example, when an anisotropically conductive sheet is used in electrical inspection for circuit devices, the anisotropically conductive sheet is interposed between a circuit device (hereinafter may be referred to as xe2x80x9ccircuit device to be inspectedxe2x80x9d) which is an inspection subject to be inspected and a circuit board for inspection, the anisotropically conductive sheet is pressurized, thereby achieving electrical connection between the circuit device to be inspected and the circuit board for inspection to conduct electrical inspection. However, an electric charge is easy to generate by pressurizing operation and separation operation, so that when the electrical inspection of a great number of circuit devices to be inspected is continuously conducted, the electric charge is accumulated on the surface of the anisotropically conductive sheet which comes to bear high-voltage static electricity.
When the electric charge is accumulated on the surface of the anisotropically conductive sheet to bear the static electricity, the circuit device to be inspected is stuck on the anisotropically conductive sheet by such static electricity. It is thus difficult to smoothly conduct the inspecting operation. When high-voltage static electricity is accumulated on the anisotropically conductive sheet, inconvenience is encountered on the security of operator""s safety. When extremely high-voltage static electricity is accumulated in particular, an adverse influence by discharge of the static electricity may be exerted on not only the inspection apparatus and the anisotropically conductive sheet, but also the circuit device to be inspected in some cases. As a result, there is a possibility that the circuit board for inspection and inspection apparatus may go wrong, or the circuit device to be inspected may be broken.
For such reasons, it is necessary to stop inspecting operation periodically or as needed at the time the generation of static electricity is observed on the surface of the anisotropically conductive sheet, so as to conduct static charge-eliminating operation by means of a static charge eliminating brush or the like. Therefore, there is a problem that inspection efficiency is lowered.
The present invention has been made on the basis of the foregoing circumstances and has as the first object the provision of an anisotropically conductive sheet capable of preventing or inhibiting it from being charged by generation of static electricity on the surface thereof.
The second object of the present invention is to provide a process for producing an anisotropically conductive sheet capable of preventing or inhibiting it from being charged by generation of static electricity on the surface thereof.
In the first aspect of the present invention, there is provided an anisotropically conductive sheet that exhibits conductivity in its thickness-wise direction, which comprises a semiconductive part that exhibits semiconductivity in the plane direction of the sheet.
In the anisotropically conductive sheet according to the first aspect of the present invention, the volume resistivity of the semiconductive part may preferably be 10xe2x88x927 to 104 xcexa9m.
The surface resistivity of the semiconductive part may preferably be 10xe2x88x92to 1010 xcexa9/xe2x96xa1 (ohm per square).
In the first aspect of the present invention, there is also provided an anisotropically conductive sheet comprising a plurality of conductive parts each extending in the thickness-wise direction of the sheet and semiconductive parts each exhibiting semiconductivity in the plane direction of the sheet and formed so as to surround each of the conductive parts.
In the first aspect of the present invention, there is further provided an anisotropically conductive sheet comprising a plurality of conductive parts each extending in the thickness-wise direction of the sheet, insulating parts formed so as to surround each of the conductive parts, and semiconductive parts each exhibiting semiconductivity in the plane direction of the sheet and formed so as to surround each of the insulating parts.
In the first aspect of the present invention, there is still further provided an anisotropically conductive sheet comprising a base sheet exhibiting semiconductivity in its plane direction and conductive particles contained in the base sheet in a state oriented so as to be arranged in the thickness-wise direction of the base sheet.
In the anisotropically conductive sheets according to the first aspect of the present invention, the semiconductive parts or base sheet may preferably contain at least one conductive substance selected from among conductive organic substances, amine type organic conductive substances, conductive polymers, metallic particles and carbon black.
In the first aspect of the present invention, there is yet still further provided a process for producing an anisotropically conductive sheet, which comprises the steps of forming a sheet-forming material layer with conductive particles which exhibit magnetism, and a semiconductivity-imparting substance contained in a polymer-forming material which will become an elastic polymeric substance by curing, applying a parallel magnetic field having an intensity distribution to the sheet-forming material layer in the thickness-wise direction thereof and subjecting the sheet-forming material layer to a curing treatment.
In the first aspect of the present invention, there is yet still further provided a process for producing an anisotropically conductive sheet, which comprises the steps of providing a sheet for semiconductive part exhibiting semiconductivity, in which through-holes or openings have been formed, forming a layer of a material for conductive part containing conductive particles, which exhibit magnetism, in a polymer-forming material which will become an elastic polymeric substance by curing, in each of the through-holes or openings in the sheet for semiconductive part, applying a parallel magnetic field or a parallel magnetic field having an intensity distribution to the layer of the material for conductive part in the thickness-wise direction thereof and subjecting the layer of the material for conductive part to a curing treatment.
In the first aspect of the present invention, there is yet still further provided a process for producing an anisotropically conductive sheet, which comprises the steps of forming a sheet-forming material layer with conductive particles which exhibit magnetism, and a semiconductivity-imparting substance contained in a polymer-forming material which will become an elastic polymeric substance by curing, applying a parallel magnetic field to the sheet-forming material layer in the thickness-wise direction thereof and subjecting the sheet-forming material layer to a curing treatment.
Since each of the anisotropically conductive sheets according to the first aspect of the present invention has the semiconductive parts which exhibit semiconductivity in the plane direction thereof, at the surface thereof, the elimination of static charge is conducted through the semiconductive parts by grounding the semiconductive parts, so that the anisotropically conductive sheet is prevented or inhibited from being charged by generation of static electricity on the surface thereof.
In the second aspect of the present invention, there is provided an anisotropically conductive sheet comprising an anisotropically conductive sheet member having conductivity in its thickness-wise direction and a static charge-eliminating layer integrally provided on at least one surface of the sheet member.
In the second aspect of the present invention, there is also provided an anisotropically conductive sheet comprising an anisotropically conductive sheet member provided with a plurality of conductive parts each extending in the thickness-wise direction of the sheet member in a state mutually insulated by insulating parts, and a static charge-eliminating layer provided on at least one surface of each of the insulating parts in the sheet member.
In such an anisotropically conductive sheet, the static charge-eliminating layer may preferably be provided on the insulating parts in the sheet member.
A recess may be formed in at least one surface of each of the insulating parts in the sheet member, and the static charge-eliminating layer may be provided in the recess.
In the anisotropically conductive sheet according to the second aspect of the present invention, the static charge-eliminating layer may preferably be composed of a layer containing a conductive organic substance, amine type organic conductive substance, metal or carbon black, a layer of a thermosetting resin or thermoplastic resin containing a conductive substance therein, or a layer formed of a conductive polymer.
The static charge-eliminating layer may preferably be formed of a metallic layer.
In the second aspect of the present invention, there is further provided a process for producing an anisotropically conductive sheet, which comprises the steps of preparing a flowable composition for forming a static charge-eliminating layer, which contains a conductive substance, coating a sheet member with the composition for forming the static charge-eliminating layer to form a coating film, and then subjecting the coating film to a fixing treatment, thereby forming the static charge-eliminating layer.
In the second aspect of the present invention, there is still further provided a process for producing an anisotropically conductive sheet, which comprises the steps of preparing a flowable composition for forming a static charge-eliminating layer, which contains a conductive substance and a binder or a curable material which will become a binder, coating a sheet member with the composition for forming the static charge-eliminating layer to form a coating film, and then subjecting the coating film to a drying treatment and/or a curing treatment, thereby forming the static charge-eliminating layer.
In the second aspect of the present invention, there is yet still further provided a process for producing an anisotropically conductive sheet, which comprises the steps of producing a film for static charge-eliminating layer to become a static charge-eliminating layer, and bonding the film for static charge-eliminating layer to a sheet member, thereby forming the static charge-eliminating layer.
In the second aspect of the present invention, there is yet still further provided a process for producing an anisotropically conductive sheet, which comprises the steps of forming a layer to become a static charge-eliminating layer on the molding surface of a mold for forming a sheet member, filling a sheet member-forming material with conductive particles contained in a polymer-forming material which will become an elastic polymeric substance by curing, into the mold to form a layer of the forming material, and subjecting the forming material layer to a curing treatment.
According to the constitution of the second aspect of the present invention, the static charge-eliminating layer is provided on one surface of the sheet member in the anisotropically conductive sheet, so that the anisotropically conductive sheet can be prevented or inhibited from being charged by generation of static electricity on the surface thereof by grounding the static charge-eliminating layer.
In the third aspect of the present invention, there is provided an anisotropically conductive sheet comprising an anisotropically conductive sheet member having conductivity in the thickness-wise direction of the sheet member and formed of an elastic polymeric substance, a conductive part for connection to be connected to an external device or terminal of an electronic part, and at least one conductive part for static-charge elimination to be connected to a ground.
In the above-described anisotropically conductive sheet, the sheet member may preferably be provided with a plurality of conductive parts for connection each extending in the thickness-wise direction of the sheet member in a state mutually insulated by insulating parts, and the conductive part for static-charge elimination may be arranged in a blank region outside a region, in which the conductive part for connection is arranged, in the sheet member.
In this case, the sheet member may be constructed by arranging at least one conductive part for static-charge elimination in a dispersive state in the blank region.
The sheet member may also be constructed by arranging at least one conductive part for static-charge elimination about the region in which the conductive part for connection is arranged.
In the anisotropically conductive sheet according to the third aspect of the present invention, the conductive parts for static-charge elimination may contain at least one conductive substance selected from among metallic particles, conductive metal oxides, conductive organic substances and carbon black.
The conductive parts for static-charge elimination may have the same structure as the conductive part for connection.
The conductive parts for static-charge elimination may have the same composition as the conductive part for connection.
According to the anisotropically conductive sheet according to the third aspect of the present invention, the sheet is connected to a ground through the conductive part for static-charge elimination, so that static electricity is eliminated through the conductive part for static-charge elimination. As a result, the sheet can inhibit static electricity from being accumulated on the surface thereof, thereby excluding an adverse influent of the static electricity on the conductive part for connection. Accordingly, the sheet can be suitably used as a connector for achieving various electrical connections.
The conductive part for static-charge elimination is arranged in the dispersive state in the blank region, whereby static electricity is eliminated through the conductive part for static-charge elimination, so that the anisotropically conductive sheet can be sufficiently inhibited from bearing static electricity throughout the blank region.
The conductive part for static-charge elimination is arranged about the region in which the conductive part for connection is arranged, whereby any discharge could be caused at the conductive part for static-charge elimination even when the static electricity is discharged on the surface of the sheet inconviniently, thereby promptly eliminating static electricity through the conductive part for static-charge elimination. Therefore, the conductive part for connection is not adversely affected.
The above anisotropically conductive sheets according to the present invention are useful as connectors and may be suitably used in testing methods for electrically inspecting circuit devices in particular.